Gap junctions formed by connexin 43 (Cx43) play an important role in transmitting signals between[unreadable] bone cells such as osteoblasts and osteoclasts, cells responsible for bone formation and bone remodeling.[unreadable] However, osteocytes express extremely large amounts of Cx43 compared with other bone cell types and this[unreadable] protein is located both on the membrane cell surface as well as in the cytoplasm. Osteocytes, unlike other[unreadable] cell types, only connect and form gap junctions with other cells through the tips of their dendritic processes.[unreadable] This is a very small percentage of the total cell surface area compared to other cells. Our data shows that in[unreadable] addition to gap junctions, primary osteocytes and osteocyte-like MLO-Y4 cells express functional Cx43-[unreadable] forming hemichannels and that these hemichannels mediate the immediate release of prostaglandin by[unreadable] osteocytes in response to fluid flow shear stress. The central hypothesis of the project based on our[unreadable] significant preliminary findings is that hemichannels formed by Cx43 have essential, yet distinct functions[unreadable] from gap junctions in the mediation and regulation of the osteocytic response to mechanical strain. Three[unreadable] specific aims will be pursued: 1). Determine the importance of Cx43 in osteocytes in vivo in response to[unreadable] mechanical strain by the generation of targeted deletion and overexpression of Cx43 in osteocytes in[unreadable] transgenic mouse models; 2). Determine the function of hemichannels in osteocytes by the specific blocking[unreadable] of hemichannel function, but not gap junction function; and 3). Determine the role alpha5 Integrin plays in the[unreadable] regulation of the opening of hemichannels induced by fluid flow shear stress. This last specific aim will be[unreadable] accomplished by blocking either expression of aSintegrin or blocking protein interaction with Cx43. One of[unreadable] the innovative aspects of this proposal is the discovery of a novel, unconventional function for hemichannels[unreadable] in osteocytes and regulation of Cx43-forming hemichannels in osteocytes in response to mechanical strain.[unreadable] Moreover, this study combines comprehensive biochemical, molecular, transgenic and functional[unreadable] approaches with unique mechanical engineering applications. It is our expectation that our experimental[unreadable] findings will have a major impact on our understanding of the novel roles hemichannels play in regulating[unreadable] osteocyte response to mechanical strain. Our experimental outcomes will be significant because the new[unreadable] knowledge obtained will contribute to our understanding of how mechanical signals are transduced and[unreadable] modulated between osteocytes and cells on the bone surface. Furthermore, completion of these three[unreadable] specific aims should provide novel contributions to the development of strategies for the treatment of bone[unreadable] diseases such as osteoporosis by providing clues for potential targets for drug action and development.[unreadable]